The mechanical ancestor of today's large combines was the McCormick reaper, introduced in 1831 and followed by self-raking reapers that delivered the cut grain in bunches on the ground to be bound by hand. In 1843 a "stripper" was brought out in Australia that removed the wheat heads from the plants and threshed them in a single operation. Threshing machines were powered first by men or animals, often using treadmills, later by steam and internal-combustion engines. The modern combine harvester, originally introduced in California about 1875, came into wide use in the United States in the 1920s and '30s and in the United Kingdom in the 1940s. In 1940 the self-propelled combine was introduced. The combine cuts the standing grain, threshes out the grain from the straw and chaff, cleans the grain, and discharges it into bags or grain reservoirs. Other crops also can be worked by adaptations of the machine, and the reduction in harvesting time and labour is striking; in 1829 harvesting one acre of wheat required 14 man-hours, while the modern combine requires less than 30 minutes. In the early part of the 19th century harvesting a bushel of wheat required three man-hours' work; today it takes five minutes.
For satisfactory results, crops should not be too damp and should be reasonably ripe. If the grain contains over 14 percent moisture, as often happens in the United Kingdom and other European countries, it must be dried after harvesting under controlled conditions to avoid damage to the gluten. Rice can be combine-harvested, but because of its high moisture content (approaching 20 percent) it must be immediately dried.
